This invention relates to a tubular member having an end coupler collar unit and particularly to a tubular member having a hardening wall for transport of mechanically abrasive and wear-creating fluid materials, in particular, fluid concrete.
Concrete pumping systems are used in placement of concrete in various applications. The present invention has been particularly applied to the concrete pumping technology but may of course be used in other pipe lines which transport like highly mechanically abrasive material. In boom mounted units, the booms are formed of tubes to form a part of the pumping line. Hereinafter, pipe is generically used to include any tubular member which is interconnected to form a part of the line. In concrete pumping, excessive wear of the pipe is a common problem, and a special problem at the coupling of the pipe sections, particularly where there is a change of flow direction.
As is well known in the art, to minimize the necessity for frequent replacement of pipe sections and particularly elbows, the pipe may be specially formed with an inner wall to withstand an abrasive characteristic, such as by specially hardening of the inner wall of the pipe or providing a highly abrasive resistance inner liner, generally including a hardened inner steel member, a suitable ceramic liner material or the like material which are abrasive resistant. An advantageous dual metal wall structure which provides a hardened and high wear resistant inner liner is disclosed in the U.S. Pat. No. 5,097,585 which issued Mar. 24, 1992 to the assignee of this invention. A similar single wall pipe is disclosed in U.S. Pat. No. 5,379,805 which issued Jan. 10, 1995.
In concrete pumping systems, initial pipe sections are interconnected to each other with releasable couplings. A typical system is disclosed in U.S. Pat. No. 3,705,737, which issued Dec. 1, 1972 and U.S. Pat. No. 4,305,607 which issued Dec. 15, 1981, to the assignee of this invention. The couplings of the pipes generally in present technology include a multiple part releasable clamp assembly such as a hinged C-shaped clamp or a bolted clamp unit and the like with a sealing gasket located within the coupling to seal the joint between slightly spaced pipe ends of the line. Thus, the pipe ends will normally be spaced slightly from each other and sealed by the outer special gasket structures. The pipe ends universally include an end body member or collar which has an annular groove, with the side edges of the U-shaped clamp members fitting within the grooves and locking the pipes to each other. Where a change of direction is required in the flow of the concrete, elbow sections are similarly connected to the straight pipe sections.
All pipe connections present areas which are particularly subject to significant wear as a result of abrasive characteristic of concrete, and will exist with other mechanically abrasive semi-solid flowing materials. The area of each pipe coupling presents on areas of significant weakness. The pipe elbows in the flow system also present a particularly severe area of wear at the outer elbow wall facing the oncoming stream of concrete as a result of the continuous engagement of the solid particles within the concrete or other particle borne fluid moving into turning engagement with such wall.
In connection with fixing of end collar assemblies or units to heat treated tubes and pipes forming a part of a concrete pumping line, the prior art has otherwise uniformly heat treated the pipe proper to harden the inner wall and thereafter welded the collar unit to the hardened pipe. Welding of the collar to the pipe however, results in tempering of the hardness of the inner wall of the pipe and thereby decreases the wear resistance of the inner wall at the pipe to the abrasive affects of the flowing concrete. Applicant has found that the problem is particularly critical in thin wall pipe which generally are known in the concrete pump art as solid wall pipes having a thickness of about one quarter inch or less as well as some of the new higher hardness type products.
In the concrete pumping art, the assignee of this invention has made available an improved end coupler unit which significantly increases the life of the coupler unit, permits on-site reconstruction of the coupler unit for continued functioning of the pipe. Generally, in the above coupler unit, a special hard wear-resistant insert liner is formed of a special hardened material, such as a special carbide material, a special ceramic material or the like. The hard wear-resistant insert liner is secured within a recessed end of the collar of the coupler unit. The insert liner is adhesively bonded in place and subject to release, using heat or another operative energy field to soften or otherwise effectively release the adhesive and permit ready removal of the insert liner as well as the adhesive. The liner maintains a highly wear resistant end in the pipe section at the interface between the two connected pipe sections, as well as creating a system for rapid and cost effective end replacement structure for extending the life of the pipe section.
Another solution which has been considered is to heat treat the pipe after the collar end is first welded in place. Applicant has found that this process eliminates or minimizes the heat effective zone with respect to hardening but problems arise due to length variance of the pipe sections. Thus, the hardening operation after welded attachment of the collar causes the microstructure of the pipe material to grow in size. This growth is erratic because the pipe product is not entirely converted to a martensite and the hardness profile may vary throughout the wall of the product. Experience with such forming of pipe without a heat effected zone has resulted in variations of +/xe2x88x92{fraction (3/16)} inches in a ten foot tube or pipe. Such a length variation is generally unacceptable in present day system.
Thus, although the various problems have been well recognized and various solutions suggested and used, there is a continuing need for cost effective solution to the problem of the wear characteristic created by the flow of abrasive materials, particularly at the pipe connecting joints.
The present invention is directed to a simple structure and manufacturing system for isolating of the heat created in welding the collar to the hardened pipe to establish and maintain optimum performance. Generally, in accordance with this invention an isolating member is interposed between the hardened pipe and the welded collar. Generally, in a preferred construction, a thin tubular sleeve member is welded to the raw pipe which is then hardened. The assembly is preferably formed of a greater length than the final length and cut to a precise length after welding the sleeve to the pipe. The coupling collar or other connecting member is then telescoped or slid over the outer end of the sleeve and welded to the sleeve. The isolating member prevents the welding of the collar in position from adversely affecting the hardness of the basic pipe structure. More particularly in accordance a practical and preferred construction of the present invention, a plurality of the pipe sections are formed from an elongated raw material pipe. The raw material pipe is equal in length to a substantial multiple of the individual pipe sections. A number of the short isolation sleeves are slipped over the elongated pipe at appropriate spacings. The plurality of so aligned sleeves are then welded to the raw material pipe. Only after such welding is the raw material pipe subject to hardening preferably through a system utilizing induction in coils with an inner quench head, with the hardening, of only the inner pipe portion. This also results in some hardening of the sleeve. As this also provides an additional hardened material in the area of the connection which is an area of significant wear, it provides for an improved and rigid joint connection in such preferred construction. A preferred system is fully disclosed in the U.S. Pat. No. 5,379,805 and is assigned to the assignee of the present invention. Because the welds were made prior to heat treating of the pipe, the weld of the sleeves does not affect the metallurgical properties of the inner hardened surface and wall portion. After the processing, the hardened pipe or tube and sleeve assembly is cut to the required lengths. Cutting is preferably provided utilizing with present day technology, a plasma torch. The plasma torch cutting is a very rapid system which minimizes any heat input to the structure being cut. A plasma torch also yields a very accurate and final length without affecting the hardened inner wall portion.
As more fully described in connection with the illustrated embodiments, the sleeve is preferably welded to define an air gap or spacement between the sleeve and the pipe. Even the most minimal air gap will provide adequate insulation to effectively isolate the welding of the collar to the sleeve from transferring any affected heat into the pipe as such and thereby prevent any adverse affect on the inner hardened wall of the pipe. Although the air gap provides a completely satisfactory isolating system, any other form of thin isolating layer or material might also be interposed between the sleeve and the pipe. It is important however, to maintain a rather rigid interconnection without any structure permitting any significant movement of the sleeve which could exaggerate any misalignment of the coupling at the connecting joint.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.